One time is certainly not a "conversion". Most (I think) would agree to say an animal is converted over, they need to take a prey item 5-10 times.
I have had several problem eaters in the past and I have employed a variety of tricks:
(1) One is as you mention, giving them a desirable prey item (in your case a mouse), then as they get close to swallowing it, place the rats head just inside the snake's open mouth and hold it there. They will grab on and swallow it. I have pretty much never had this method fail. However, it does not necessarily help transition the snake from one prey species to another. Sometimes it works, sometimes you will have to continuously do it.
(2) As far as "scenting", I have found rubbing on prey animal on another does not usually work at the beginning. A more effective way is to cut off a piece of the desirable prey species and place it over the head of the feeder. For example, in lizard-eating species, I would place a section of anole skin over the nose of the mouse and this would trigger a feeding response. Blood scenting can also work.
After doing this 3-4 times, lighter scenting, such as simply rubbing the desirable prey item on the feeder item usually starts to work as they transition over. Eventually, they will take the new feeder item.
(3) The other thing you can do, which often works with ball pythons in particular, is to place the F/T feeder item underneath/inside the warm hide. This serves the dual purpose of keeping the feeder item warm and providing extra security for feeding. I actually have one ball python that will exclusively eat this way.